Wave-transmission system



March 10, 1931. c, DICKIESQN 1,795,479

WAVE TRANSMISSION SYSTEM Filed Oct. 30, 1926 Af/amey Patented Mar. 10,1931 UNITED STATES PATENT OFFICE ALTON C. DICKIESON, OI BBOOKLYN, NEWYORK, ASSIGNOB TO BELL TELEPHONE LABO- RATORIES INCORPORATED, OF NEWYORK, N. Y., A CORPORATION OF NEW YORK WAVE-TRANSMISSION SYSTEMApplication filed October 30, 1926.

This invention relates to Wave transmission systems and particularly tomeans tor controlling the energy level of transmission in such systems.

An object of the invention is to control the energy level in a signalingsystem in response to changes in the intensity of the transmitted waves.

Other objects of the invention are to increase the sensitivity andprecision of volume control systems.

The invention is especially applicable to radio broadcasting, publicaddress and similar systems, where music and speech are 1'5 transmittedover telephone or other transmission circuits. A feature of theinvention is a simple and efiicient circuit for automatically regulatingthe energy level.

Heretofore, this has usually been accom- 2o plished by connecting avolume indicator across the outgoing line to indicate changes in theenergy level of the transmitted waves. An operator observes thedeflection of the volume indicator and manually adjusts the gain of anamplifier in the outgoing line to obtain the desired energy level.

Recent inventors have provided automatic systems of volume control whichrequire little or no maintenance and also eliminate the elew ment ofinaccuracy which usually exists in manually controlled systems. A systemwhich is typical of the recent advance in the art is disclosed in aUnited States Patent 1,690,224 to E. W. Gent, patented November '35 6, 1928, in which the gain of a thermionic amplifier is varied in responseto changes in the amplitude of the transmitted currents. The presentinvention is a result of attempts to simplify the construction andoperation of automatic volume control systems.

The volume control circuit of this invention includes a Vheatstonebridge having a pair of opposite terminals connected to an incoming lineand the other pair of opposite terminals connected to an outgoing line.One arm of the bridge includes a device which responds to variations inthe strength of the incoming currents to control the condition of thebridge. The bridge is normally unbalanced so that it passescomparatively Serial No. 145,171.

Weak currents with little or no attenuation. When the amplitude of the.incoming currents increases, however, the bridge becomes more nearlybalanced and hence introduces an increasing loss into the circuit.Variations in the amplitude of the incoming cur rents thus effect acompensating change in the transmission loss of the circuit and theenergy level is maintained substantially constant.

A feature of the invention resides ina highly sensitive bridge circuitwhich may be employed as a volume compressor, but may also be used forother purposes. One arm of this bridge includes the contacts of a voiceoperated relay, the resistance characteristics of which are such thatthe resistance remains substantially constant for input amplitudeswithin a certain definite range, while beyond this range the contactresistance increases rapidly.

The invention will be described in connection with the accompanyingdrawing in which similar reference characters represent correspondingparts in the different figures, and in which:

Fig. 1 is a diagrammatic illustration of a volume control systememploying the sensitive bridge circuit of the invention;

Fig. 2 shows a curve illustrating the contact resistance characteristicsof the relay shown in Fig. 1; and

Fig. 3 is a diagrammatic illustration of a modified volume controlsystem.

In Fig. 1, an incoming circuit 5 is connected to the opposite terminals6 and 7 of a WVheatstone bridge 8. The other two opposite terminals 9and 10 of the bridge are connected to an outgoing circuit 11. One arm ofthe lVheatstone bridge includes the contact device 12 of a low frequencyvibrating relay 13 having its windings connected across the incomingcircuit 5. This relay is preferably oi. the type disclosed in U. S. Patent No. 1,579,887 to E. J. Pratt, issued April 6, 1926.

The contact resistance characteristics of the relay 13 are illustratedgraphically by the curve of Fig. 2, in which the ordinates represent thecontact resistance and the abscissae represent the voltage impressedupon the windings of the relay from the circuit 5. It will be seen fromthis curve that the contactresistance is negligible up to a certaindesired low input voltage, and then increases and remains substantiallyconstant over a fairly wide range of voltages, and beyond the upperlimit of this range the resistance increases rapidly.

The circuit is so adjusted that'the Wheatstone bridge is completelyunbalanced when no signals are impressed upon the windings of the relay13. comparatively weak signal voltages produce no efiiect upon thecontact resistance, as shown by the curve of Fig. 2, and are thereforepractically unattenuated in passing through the bridge. When theimpressed voltage increases above a predetermined limiting value,however, the relay 13 begins to operate and the contact resistanceincreases. This increase in resistance tends to make the Wheatstonebridge more nearly balanced and limits the voltage impressed upon theoutgoing circuit 11. As a result of this action, excessive voltages inthe incoming circuit 5 are prevented from reaching the outgoing circuit11 and the outgoing signals are maintained at a substantially constantenergy level.

The modified volume control system shown in Fig. 3 includes a sensitiveresponse circuit of the type disclosed in my copending applicationSerial No. 145,170, filed October 30, 1926, which was issued as Patent1,762,768, June-10, 1930. This circuit includes an amplifier A havingits input connected across the circuit 5 and its output coupled by meansof transformer 14: to the grid circuit of 'a three-electrode spacedischarge tube rectifier 15. The plate circuit of the rectifier 15 isincluded in one arm of the VVheat'stone bridge between the terminals 6and 10. The grid of the rectifier 15 is given a negative bias such thatsmall changes in the biasing potential produce large changes in theresistance of the plate circuit. The constants of the circuit are sochosen that the bridge is normally unbalanced and offers littleresistance to the passage of weal; signals. As the voltage impressedupon the grid circuit of the rectifier 15 increases, however, theresistance oi the plate circuit increases greatly and tends to make thebridge more nearly balanced, the operation being substantially the sameas that of the system of Fig. 1.

The invention is also capable of other modiiications and adaptations notspecifically referred to but included within the scope of the appendedclaims.

\Vhat is claimed is:

1. A wave transmission system comprising an incoming circuit, a sourceof waves therein of varying volume, an outgoing circuit, a lVheatstonebridge having two opposite terminals connected to said incoming circuitand the other two opposite-terminals connected to said outgoing circuit,said bridge being normally unbalanced to permit waves of low volume topass freely from said incoming to said outgoing circuit, said bridgeincluding a variable resistance in one arm and means connected to theincoming circuit and responding to volume variations in the incomingwaves for continuously varying said re sistance over a range of volumevariations in said waves to control the degree of unbalance of saidbridge circuit.

2. A wave transmission system comprising a circuit for transmittingelectrical waves, a lVheatstone bridge for controlling the transmissionof said waves through said circuit, an electromagnet responsive tochanges in the amplitude of said waves, and a variablere sistancevibrating contact element controlled by said electromagnet and havingits contact resistance included in one arm of said bridge, said contactresistance being a functionof the response characteristic of saidelectromagnet and determining the degree of unbalance of said bridge.

3. A wave transmission system comprising a circuit for transmittingelectrical waves, a lVheatstone bridge the degree of .unbalance of whichdirectly controls the volume of transmission of said waves through saidcircuit, and a vibrating relay responsive to changes inthe amplitude ofsaid waves, the the contact resistance of said relay directlycontrolling the condition of balance of said bridge.

v 4. A wave transmission system comprising an incoming circuit forreceiving wave energy of varying volume, an outgoing circuit, aWheatstone bridge having two opposite terminals connected to saidincoming circuit and the other two opposite terminals connected to saidoutgoing circuit, and a relay quantitatively responsive to changes inthe volume of said incoming wave energy, said relay controllingquantitatively the degree of unbalance of said bridge.-

5. A Wave transmission system comprising an incoming circuit forreceiving wave energy of varying volume, an outgoing circuit, aWheatstone bridge having two opposite terminals connected to saidincoming circuit and the other two opposite terminals connected to saidoutgoing circuit, a relay responsive to changes in the volume of saidincoming wave energy, and a vibratile contact element controlled by saidrelay and forming at least part of the resistance of one of the arms ofsaid bridge, said relay quantitatively controlling the degree ofunbalance of said bridge.

6. A sensitive response circuit comprising a Wheatstone bridge, meansfor applying variable voltage thereto, an electromagnet responsive tovariations in said voltage, and means for varying the resistance of anarm of said bridge to vary the degree of unbalance of the bridge,including a vibratile contact controlled by said electromagnet andhaving substantially constant resistance for applied voltages below apredetermined limit but the 5 resistance of which rises rapidly abovesuch limit.

7 In an electrical transmission system, a Wheatstone bridge comprisingfixed resist ance arms and a variable arm, the resistance 10 of which isinstantaneously variable under control of volume variations intransmitted energy, an input circuit and an output circuit connectedrespectively to opposite diagonals of said bridge, and means forutilizin a portion of the input for directly controlling the resistanceof said variable arm.

8. A sensitive response circuit comprising a Wheatstone bridge, and arelay having a vibratile contact included in an arm of said bridge tocontrol the balance thereof, the resistance of said vibratile contactbeing a continuous function of the response of the relay to changes inthe voltage applied to said circuit.

9. A sensitive response circuit comprising a Wheatstone bridge which isnormally unbalanced, an input and an output circuit connectedrespectively to the opposite diagonals of said bridge, and a relayhaving a vibratile contact connected in one arm of said bridge, theresistance of said vibratile contact being a continuous function of theresponse of the relay to changes in the voltage applied to said circuit.

In witness whereof, I hereunto subscribe my name this 22nd day ofOctober, A. D.,

ALTON C. DICKIESON.

